The present invention relates generally to dosing mercury in discharge lamps. More specifically, the present invention relates to dosing a small quantity of mercury into the light emitting chamber of a discharge lamp using solid mercury-containing dispensers in the form of particles of high purity, uniform size, and uniform composition.
Discharge lamps such as cold cathode fluorescent lamps having a vaporizable lamp fill including mercury are commonly used for computer display backlighting and instrumentation illumination such as in an automobile or airplane. In the manufacture of such discharge lamps, it is necessary to introduce very small amounts of mercury into the light emitting chamber of the lamp. For example, a cold cathode fluorescent lamp typically includes about 0.1 mg up to about 10 mg of mercury depending on the size of the lamp. However, some discharge lamps may require as little as 0.001 mg or as much as 50 mg of mercury. While it is possible to introduce liquid mercury directly into the chamber, it is very difficult to obtain precise doses of such small quantities of mercury using this method due to the high surface tension of mercury. Consequently, lamps dosed by this method usually include more mercury than is needed for operation of the lamp leading to concerns with meeting government regulations on mercury content and to environmental concerns in the disposal of the lamps. Direct introduction of liquid mercury into the chamber may also be impeded by retention of small droplets of mercury on the surface of the dosing tube.
There remains the practical question of how to dose such small quantities of mercury into the light emitting chamber of a discharge lamp. It is known to dose the mercury using an amalgam which releases mercury when the temperature of the amalgam is elevated. For example, U.S. Pat. No. 3,957,328 to van der Wolfe et al. discloses a method of dosing mercury into the light emitting chamber of a lamp wherein an indium amalgam in a liquid or paste form is introduced and spread about the interior surface of an exhaust tube to increase the surface area thereof, and then the exhaust tube is connected in fluid communication with the light emitting chamber of the lamp. The amalgam is heated to effect release of the mercury from the amalgam into the chamber, leaving the dispensed indium in the exhaust tube for removal from the lamp therewith.
The method disclosed by van der Wolfe et al. suffers from several disadvantages. The amalgam is in the form of a liquid or paste and thus the precise amount of amalgam must be measured prior to introducing the amalgam into the exhaust tube of the lamp. Further, the amalgam must be introduced into the exhaust tube with the aid of a syringe and then the glob of amalgam must be spread evenly about the inner surface of the tube. The spreading of the amalgam requires rotation of the tube and, in some instances, a jet of gas such as air is required to sufficiently spread the amalgam.
To further facilitate the spreading of the amalgam in the exhaust tube, the amalgam is introduced into the tube separate from the lamp prior to connecting the tube in fluid communication with the light emitting chamber of the lamp. Certain process steps in the manufacture of the lamp must be performed after the connection of the exhaust tube (containing the amalgam) and require parts of the lamp to be exposed to high temperatures. Thus the amalgam may be exposed to high temperatures during certain lamp process steps which may lead to premature release of mercury from the amalgam, and cooling of the amalgam may be required to prevent premature release of the mercury.
Still further, the amalgam paste is susceptible to contamination by air and moisture which may lead to the introduction of contaminates into the chamber during release of the mercury.
Thus there remains a need for a method of dosing small quantities of mercury into discharge lamps in an easily fabricated and dosed solid mercury-containing dispenser of high purity, uniform size, and uniform composition.
Accordingly, it is an object of the present invention to obviate the deficiencies of the known prior art and to provide a novel mercury-containing dispenser and method.
It is another object of the present invention to provide a novel particle suitable for dispensing small quantities of mercury into a discharge lamp.
It is yet another object of the present invention to obviate the deficiencies of the known prior art and to provide a novel method of dosing mercury into a discharge lamp.
It is still another object of the present invention to provide a novel method of dosing a discharge lamp with small quantities of mercury dispensed from a solid amalgam particle.
It is a further object of the present invention to provide a method of dosing a lamp with small quantities of mercury which reduces the introduction of impurities into the lamp.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.